Alkali treatment of oil



United States 7 Patent M This invention relates to alkali treatment ofhydrocarbon oil and more particularly provides an improved method forthe treating of gas oil to obtain an exceptionally clear product havingunusual color and oxidative stability.

Treating processes involving the use of relatively strong, aqueousalkali metal hydroxide solutions containing upwards of 35% by weightalkali metal hydroxide are being widely used to reduce sulfur contentand to improve color, odor and oxidative stability, and inhibitorresponse of gas oil fractions, particularly catalytically cracked gasoil fractions. The alkali treatment removes, along with mercaptans,acidic organic materials (sometimes described as acid oils) includingvarious phenols and cresols and other alkyl phenols. The oil-solublealkyl phenols and other organic acids react with strong caustic to formoilinsoluble products which are thus readily separable from the oilphase. The acid oils are known to have a pronounced efiect on colorstability and their removal or substantial removal improves considerablythe color stability of the oil.

In the practice of the concentrated alkali treatment the treatingsolution is usually recirculated, although the caus-' tic treatingsolution may be used once and discarded. Recirculation of the caustic isgenerally favored in order to economize on the treating material as muchas possible} A single pass caustic treatment requires considerably moresupervision than the recycle operation if waste of caustic is to beavoided.

A typical alkali recirculation treatment involves mixing the gas oilwith a concentrated caustic solution. The mixture is passed to asettling vessel which may be of an electrical precipitator type. The gasoil-caustic solution mixture in the settling vessel separates to formtwo or three phases, depending on the process being carried out, theupper phase in each instance being a separated oil requiring furthertreatment. In the three-phase operation the mixture separates to producean upper layer of treated oil, a middle layer containing caustic andextracted organic salts, and a lower layer constituting the unspentcaustic solution. The lower unspent caustic layer, and in some instancesa portion of the middle layer, is recirculated, after addition of freshcaustic, to the inlet of the settling vessel where the recirculatedmaterial is mixed with a further amount of the oil being treated.

Ih both two-phase and three-phase conventional operations the treatedoil of the upper layer is' removed from the settling vessel and waterwashed, this being commonly achievedby mixing the wash water and oil ina mixer and introducing the mixture into a settler or into an electric,treater where the wash Water is separated from the oil product. TheWater wash is employed to remove;

from the treated oil the residual dispersed phase of the treatingsolution made up of aqueous caustic and dissolved organic salts. Suchwater washing has been found essential in the commercial operation ofthe above-de' 3,180,821 Patented Apr. 27, 1965 caustic and dissolvedorganic salts is caused to separate virtually completely from thetreated oil. The separating force can best be induced in a highlyeffective electric treater wherein the caustic treated gas oil issubjected to the action of a high-voltage unidirectional electrostaticfield of a voltage gradient of at least about 7 kv./inch. The physicalforce required for the separation of the dispersed phase from thetreated oil may, in an alternative, be provided by subjecting the gasoil to a centrifugal force in excess of about 850 gs and preferably inexcess of about 950 gs for a time suflicient to separate the oil and itsdispersed phase virtually completely, for example, a centrifugal forceof about 8504000 gs or more for respective times of at least 30-10minutes.

The improved process of the invention is especially suitable for thealkali treatment of catalytically cracked gas oil boiling in the rangeof about 425675 F. to provide a product having exceptional colorstability. This unexpected improvement in color stability isattributable to the elimination of all the residual dispersed materialwhich contains salts of acidic organic materials removed rom the gas oilproduct. The caustic treated oil issuing directly from the causticsettlingvesse'l contains a dispersed phase made up of alkali metalphenolates, such as alkali metal cresylate, and other water solubleorganic salts dissolved in a small amount of the aqueous caustic. Whenthe oil containing the dispersed phase is washed with water inconventional processing, hydrolysis of some of the organic salts occurs,with the result that these salts are returned to their oil soluble acidform and are dis solved back into thef oil phase, thereby being presentto degrade the color stability of the oil.

In the process of the invention, the gas oil is mixed withan amount ofstrong aqueous solution of alkali metal.

hydroxide sufiicient to react with the acidic organic materials of theoil and form salts therewith- The alkali metal hydroxide normally makesup about 35-50% of the aqueous solution by weight. The aqueous alkalisolution is then separated from the oil, producing a body of treated oilcontaining a small residual dispersion of caustic and organic acidsalts.

, superdehydrating step as the sole treatment for removing duced by theprocess of the invention is the great re-. duction in "haze point of thetreated oil. In the conventional method of operation, the final waterWash produces an oil which is not only saturated with water, but also 1contains a residual haze due to the presence of very finely dividedWater droplets. This produces an oil of poor marketability because ofcustomer objection to its appearance as Well as the deleterious effectsof the water present, which can promote corrosion, plugging of fuel jetsand other undesirable results. A caustic treated gas oil which has beenWater washed will usually have a clarity of 65 to 95, asmeasured bypercent light transmission in the conventional way (green filter). Onthe other hand,

an oil produced in accordance with the process of the in vention willnormally have a'clarity of 100. Even if such a residual haze "isremoved, such as by extended settling; periods etc., the oil beingsaturated withwater at the op-I crating temperature (usually F.) 'Willform a haze as soon as it is cooled only slightly (say 5 F.) below This,of course, is highly.

such operating temperature.

undesirable as indicated above. Thehaze point of the caustic treatment.a V

'An oil pr oduced in accordance with the process of the invention Willusually exhibit a significant improvement The separated oil is subjectedto a.

in color stability. Gas oils produced in accordance with the process ofthe invention will normally have an initial A.S.T.M. color not darkerthan 2 /2 and usually an A.S.T.M. color close to 1 /2, depending uponthe particular oil source and processing steps. The initial A.S.T.M.color of the oil of the invention Will approximate that ofconventionally caustic processed oil. Storage of the gas oil produced inaccordance with the improved process in a glass bottle at 212 F. fortwenty-four hours will normally result in an increase in A.S.T.M. colorof only /2 to 1 /2 units, compared with a similar storage ofconventional processed oil which will usually exhibit an increase inA.S.T.M. color of 1 to 2 /2 units.

The operating conditions of the caustic treating step of the process ofthe invention need not vary from those conditions normally employed,whether the process be of a recirculation type or a one-pass treatment.The solution strength of the alkali metal hydroxide, which may be eithersodium or potassium hydroxide should be in excess of 35% by Weight. Thetreating solution preferably contains the alkali metal hydroxide on aweight percentage in the range of about 35-50%. For a recirculation typetreatment, the volume percentage of caustic treating solution ispreferably about 5% of the volume of oil. A single-pass caustictreatment will employ a lower volume percent (gauged to the amount ofacid oil present) of the caustic treating solution. The temperature ofoperation is Within the range of that normally employed, beingpreferably about 100 to 150 F. The settling vessel for the caustic-gasoil mixture may be of an electrical precipitator type, although this isnot necessary.

Where superdehydration is achieved by subjecting the caustic treated gasoil to the action of a high-voltage unidirectional electrostatic field,the prime requirement of the electrical treater is that it be capable ofproviding a voltage gradient of at least about 7 kv./inch, the voltagegradient being a value resulting from dividing (a) the voltage appliedbetween spaced electrodes to establish an electric field therebetween by(b) the spacing of the electrodes in inches. A highly efficient electrictreater suitable for this use is that shown and described in US. PatentNo. 2,855,356, Stenzel. Another treater of somewhat dilferent designthat may be employed is disclosed in copending application of Stenzeland Turner, Serial No. 64,574, now abandoned. In such a treater thesuperdehydration is elfected during rise of the treated oil alonginterelectrode spaces between electrodes spaced about 2 to 8 inches andenergized from a source of undirectional high-voltage potentialsufiicient to establish a voltage gradient of at least about 7 kv./inchin the interelectrode space. If superdehydration is achieved bycentrifugal force there are numerous centrifuges commercially availablecapable of providing the high centrifugal force needed for separatingthe dispersed phase from the caustic treated oil. Either the electricalor centrifugal treatment will reduce the concentration of the dispersedphase in the oil to less than about 10 ppm. and frequently to less than1 ppm. This corresponds to values, expressed as NaOH, of 4 and .4 ppm.

Example I The oil processed in this example was a light catalytical- 1ycracked cycle oil having an API gravity of 28.6. The oil was treatedwith a recirculated caustic stream having a strength of 45 Baum. Thecaustic treating solution was used in 5% volume of the oil treated andthe treatment was carried on at 150 F. The settling vessel employed forthe separation of the treating solution and oil was of a conventionalelectrical precipitator type treating the mixture in a unidirectionalelectric field of 6 kv./inch. The caustic treated oil from the settlingvessel was divided into two portions with a first portion beingsubjected to a conventional water washing with 5 volume percent of washwater. A second portion of the caustic treated oil was superdehydrated,without water washing, in a cellular Example II In this examplecatalytically cracked cycle oil with an API gravity of 26.5 was treatedon a once-through basis with a 45 Baum caustic solution, there being norecycle of the treating solution. The treating solution was used in avolume percent adequate to supply the sodium hydroxide in an amountapproximately equivalent to the acid oils present in the cycle oil. Thetreatment was carried on at a temperature of 120 F. The caustic-cycleoil mixture was separated in an electric precipitator settling vesselwhich was supplied with an electrical gradient of 6 kv./inch. Thecaustic treated gas oil from the electric precipitator settling vesselwas divided into a first portion which was water washed in theconventional fashion with a 5 volume percent of water and a secondportion of the caustic treated gas oil which was passed to a cellularelectrical treater (there being no water addition) of the type disclosedin copending application Serial No. 64,574, Stenzel and Turner. Aunidirectional voltage gradient of 8 kv./inch was used in thesuperdehydrating cellular electrical treater. There was a trace carryover of water in the gas oil product which was water washed and thisproduct exhibited a clarity (light transmission, percent) of 96. Thesuperdehydrated gas oil product had a nil carry over and a clarity of99. Samples of the untreated raW oil, the water washed caustic treatedoil, and the superdehydrated caustic treated oil were subjected to acolor stability test which involved holding the samples in glass bottlesfor 24 hours at 212 F. The raw untreated oil at the end of theaccelerated storage test exlubited an A.S.T.M. color of 4, the waterwashed caustic treated oil an A.S.T.M. color of 4, and thesuperdehydrated caustic treated oil an A.S.T.M. color of 2+. Theaccelerated color stability test of this example clearly illustrates theimproved alkyl phenol removal obtainable with the practice of theprocess of the invention.

Example III A light catalytically cracked cycle oil having an APIgravity of 32.2 was mixed with 0.1 volume percent (an amountapproximately equivalent to the amount of acid oil present in the oil)of a 50 Baum caustic solution. This was a one-pass caustic treatmentwith no recycle. The mixture was passed to an electric precipitator andsubjected to treatment in a unidirectional electric field of a gradientof 6 kv./inch where the treated oil was separated from the causticsolution. One portion of the caustic treated oil from the electricprecipitator was washed with 7.5 volume percent of water in conventionalfashion. 'A second portion of the caustic treated oil wassuperdehydrated with no water washing in a cellular electrical treaterin a unidirectional electric field of a gradient of 8 kv./ inch. TheWater washed product had a clarity of 94 and an alkyl phenolconcentration of 2.7 ppm. In comparison, the superdehydrated product hada clarity of and an alkyl phenol concentration of 1.9.

Although exemplary embodiments of the invention have been disclosedherein for purposes of illustration, it will be understood that variouschanges, modifications, and substitutions may be incorporated in suchembodiments without departing from the spirit of the invention asdefined by the claims which follow.

. I claim: 7

1. A process for the alkali treatment of catalytically cracked gas oilboiling in the range of about 425-675 F. to remove acidic organicmaterials therefrom while avoiding hydrolysis of residual saltsfollowing separation of the alkali and producing refined products thatare bright, of

reduced haze point and of improved color stability, which processincludes the steps of:

(a) mixing with such catalytically cracked gas oil boiling in such rangean amount of strong aqueous solution of alkali metal hydroxidesuflicient to react with such acidic organic materials of the oil andform oilinsoluble salts therewith,

(b) the strength of said solution being between about 35-50% by weight;

(c) separating said solution and the salts from the oil to produce abody of separated oil made upof a continuous oil phase and a dispersedresidual aqueous phase comprising aqueous particles dispersed in theoil, said dispersed aqueous particles containing residual water solubleorganic salts resulting from the reaction of said alkali metal hydroxidewith said acidic organic materials;

(0!) and then directly and intensively dehydrating said separated oil inthe absence of hydrolysis of said organic salts to produce a treated oilcontaining no more than about p.p.m. of aqueous material, saiddehydration being effected by subjecting a stream of said separated oilcontaining residual salts to a high centrifugal force of the order of atleast about 850 gs for a time sufiicient to separate substantially allthe residual aqueous salts and produce said treated oil containing nomore than about 10 p.p.m. of aqueous material. 7

2. A process for the alkali treatment of catalytically cracked gas oilboiling in the range of about 425-675 F. to remove acidic organicmaterials therefrom while avoiding hydrolysis of residual saltsfollowing separation of the alkali and producing refined products thatare bright, of reduced haze point and of improved color stability, whichprocess includes the steps of:

(a) mixing with such catalytically cracked gas oil boiling in such rangean amount of strong aqueous solution of alkali metal hydroxidesuflicient to react with such acidic organic materials of the oil andform oilinsoluble salts therewith,

(b) the strength of said solution being between about 35-50% by weight;

(0) separating said solution and the salts from the oil to produce abody of separated oil made up of a continuous oil phase and a dispersedresidual aqueous phase comprising aqueous particles dispersed in theoil, said dispersed aqueous particles containing residual water solubleorganic salts resulting from the reaction of said alkali metal hydroxidewith said acidic organic materials;

(d) and then directly and intensively dehydrating said separated oil inthe absence of hydrolysis of said organic salts to produce a treated oilcontaining no more than about 10 p.p.m. of aqueous material, saidintense dehydration being effected by an efiicient electric dehydrationstep comprising subjecting a stream of the separated oil in aninterelectrode space to the action of a high-voltage unidirectionalelectrostatic field of a voltage gradient at least about 7 kv./inch.

3. In a treating process of the type employing a strong aqueous treatingsolution of an alkali metal hydroxide with the hydroxide constituting35% or more by weight to remove acidic organic materials from a gas oilfraction, said acidic materials being removed as oil-insoluble alkalimetal organic salts in the treating solution, and wherein the treatedoil, following separation from the treating solution, is customarilywater Washed to remove therefrom a dispersed phase of treating solutionand dissolved organic salts, the improvement comprising subjecting thetreated and separated gas oil to an intense dehydration treatmentsuflicient to cause the material of the dispersed phase to separate fromthe oil-without use of the customary water wash to obtain an oil producthaving a haze point at least 30 F. below the temperature of the process,the intense dehydration of the separated gas oil being effected bysubjecting same to a centrifugal force of at least about 850-1,000 gsfor respective times of at least 30-10 minutes and sufiicient toseparate substantially all of the dispersed phase material therefrom toproduce a treated oil containing less than about 10 p.p.m. residualdispersed phase material.

4. In a treating process of the type employing a strong aqueous treatingsolution of an alkali metal hydroxide with the hydroxide constituting35% or more by weight to remove acidic organic materials from a gas oilfraction, said acidic materials being removed as oil-insoluble alkalimetal organic salts in the treating solution, and wherein the treatedoil, following separation from the treating solution, is customarilywater washed to remove therefrom a dispersed phase of treating solutionand dissolved organic salts, the improvement comprising subjecting thetreated and separated gas oil to an intense dehydration treatmentsufiicient to cause the material of the dispersed phase to separate fromthe oil without use of the customary water wash to obtain an oil producthaving a haze point at least 30 F. below the temperature of the process,the intense dehydration of the separated gas oil being elfected bysubjecting the separated gas oil while in an interelectrode space to theaction of a high-voltage unidirectional electrostatic field of a voltagegradient at least about 7 kv./inch.

References Cited by the Examiner UNITED STATES PATENTS ALPHONSO D.SULLIVAN, Primary Examiner.

1. A PROCESS FOR THE ALKALI TREATMENT CATALYTICALLY CRACKED GAS OILBOILING IN THE RANGE OF ABOUT 425-675*F. TO REMOVE ACIDIC ORGANICMATERIALS THEREFROM WHILE AVOIDING HYDROLYSIS OF RESIDUAL SALTSFOLLOWING SEPARATION OF THE REDUCED HAZE POINT AND OF IMPROVED COLORSTABILITY, WHICH PROCESS INCLUDES THE STEPS OF: (A) MIXING WITH SUCHCATALYTICALLY CRACKED GAS OIL BOILING AN SUCH RANGE AN AMOUNT OF STRONGAQUEOUS SOLUTION OF ALKALI METAL HYDROXIDE SUFFICIENT TO REACT WITH SUCHACIDIC ORGANIC MATERIALS OF THE OIL AND FORM OILINSOLUBLE SALTSTHEREWITH, (B) THE STRENGTH OF SAID SOLUTION BEING BETWEEN ABOUT 35-50%BY WEIGHT; (C) SEPARATING SAID SOLUTION ON THE SALTS FROM THE OIL TOPRODUCE A BODY OF SEPARATED OIL MADE UP OF A CONTINUOUS OIL PHASE AND ADISPERSED RESIDUAL AQUEOUS PHASE COMPRISING AQUEOUS PARTICLES DISPERSEDIN THE OIL, SAID DISPERSED AQUEOUS PARTICLES CONTAINING RESIDUAL WATERSOLUBLE ORGANIC SALTS RESULTING FROM THE REACTION OF SAID ALKALI METALHYDROXIDE WITH SAID ACIDIC ORGANIC MATERIALS; (D) AND THEN DIRECTLY ANDINTENSIVELY DEHYDRATING SAID SEPARATED OIL IN THE ABSENCE OF HYDROLYSISOF SAID ORGANIC SALTS TO PRODUCE A TREATED OIL CONTAINING NO MORE THANABOUT 10 P.P.M. OF AQUEOUS MATERIAL, SAID DEHYDRATION BEING EFFECTED BYSUBJECTING A STREAM OF SAID SEPARATED OIL CONTAINING RESIDUAL SALTS TO AHIGH CENTRIFUGAL FORCE OF THE ORDER OF AT LEAST ABOUT 850 G''S FOR ATIME SUFFICIENT TO SEPARATE SUBSTANTIALLY ALL THE RESIDUAL AQUEOUS SALTSAND PRODUCE SAID TREATED OIL CONTAINING NO MORE THAN ABOUT 10 P.P.M. OFAQUEOUS MATERIAL.